A. Field of the Invention
This invention relates to a new or improved fuel supply system for an internal combustion engine, to a manifold specifically designed for use in such system, to a kit of parts to enable retrofitting of such system in an existing engine and to a method of controlling the fuel supply to achieve the improved response to a number of environmental conditions.
B. Description of the Prior Art
In internal combustion engines having carburetor controlled fuel supplies, as is typical of engines used in vehicles such as snowmobiles and personal watercraft, it is well known that the rate of fuel flow in a fixed or variable venturi carburetor is dependent upon the pressure differential existing in the fuel system between the venturi and e.g. a fuel bowl (otherwise called a float bowl or a float chamber). In a conventional float bowl carburetor the pressure differential is measured between the pressure in the fluid float chamber (which is normally atmospheric pressure) and the pressure at the discharge orifice of the fuel metering system which is normally located in or adjacent the venturi in the induction passage.
For optimum combustion, the relationship between the mass air flow and the mass fuel flow delivered to the engine by the carburetor should be kept constant, and to achieve this the carburetor employs either a fixed or a variable venturi (or some equivalent structure) such that when air velocity in the induction passage is increased a pressure reduction (often called a vacuum) is created in the venturi zone. This pressure reduction creates a pressure differential between the induction passage and the fuel in the float chamber, causing fuel to be drawn into the induction passage at a flow rate that is proportional to the pressure differential.
The amount or level of the venturi underpressure or vacuum is mainly a function of air velocity through the induction passage, but as is well understood, at a given velocity, the mass air flow rate is affected by air density which in turn is mainly a function of barometric pressure and air temperature.
For example for a snowmobile operating at an altitude of 2000 meters, a given air velocity in the carburetor induction passage will deliver a very much reduced mass air flow to the engine as compared to the same air velocity when the snowmobile in operating at seal level, this being due to the reduced barometric pressure and air density at altitude. However since fuel flow is mostly a function of the venturi underpressure or vacuum, the engine when operating at altitude would tend to be supplied with a mixture that is over rich in fuel. This phenomenon is well understood. For example U.S. Pat. No. 5,021,198 Bostelmann discloses a carburetor system that is designed to adjust the fuel flow to maintain the mass air fuel mixture ratio constant despite changes in altitude.